Magnetic particles are employed in various methods as a solid phase on whose surface a reaction is allowed to occur. A particle is typically coated with a substance having a specific reaction with a given second substance. This allows separation of this second substance from a mixture in which it is contained.
The particles usually need to be separated from the reaction mixture after the reaction. This has been conventionally done by removing the reaction medium from the vessel and by leaving the particles in the vessel.
WO 94/18565 discloses a method and a device for separating particles by removing them from a vessel. This is done with the aid of an elongated remover comprising a magnet located within a casing and movable in it in the longitudinal direction. As the remover is introduced into a mixture with the magnet in lower position, the particles adhere to the surface of the remover and can thus be removed from the mixture. By contrast, as the magnet is pulled into upper position, the particles are detached from the surface of the remover. The device may comprise a plurality of removers operating in parallel so as to allow simultaneous treatment of a plurality of samples. WO 96/12958 discloses a similar remover, whose magnet has a length such that only the lower pole of the magnet collects particles. Such separating techniques have also been commercially implemented in the KingFisher® separating devices of Thermo Electron Oy, Finland. These devices comprise a plurality of removers disposed in parallel, with their magnets oriented in the same direction, i.e. with similar poles always oriented in the same direction.